Plasma-mediated thermo-electric cutting for surgery is well known, see for instance, Palanker U.S. Pat. Nos. 6,135,988 and 6,780,178. See also Eggers et al. U.S. Pat. Nos. 6,047,700 and 5,697,882. These disclose plasma-mediated cutting of soft biological tissue where the tissue is immersed or profused with saline solution which, of course, is an electrically conductive medium. See also Palanker et al. U.S. Pat. No. 7,238,185 and McClurken et al. U.S. Pat. No. 7,115,139. For instance, Palanker et al. U.S. Pat. No. 7,238,185 discloses apparatus and method for cutting biological tissue where the tissue being cut is submerged in a conductive liquid medium. The cutting apparatus has a cutting electrode and a return electrode. Both electrodes are immersed in the conductive medium and a voltage (signal) applied between them in order to heat the medium, thus producing a vapor cavity around the cutting portion of the blade and ionizing a gas inside the vapor cavity to produce a plasma.
However, in actual surgical procedures such as carried out on people or animals, often the tissues are not immersed in a naturally occurring conductive medium such as blood or internal bodily fluids. Then typically a conductive medium such as saline solution is introduced as part of the surgical procedure (“wet field” electrosurgery). Typically the saline or other conductive medium is introduced onto or into the surgical field as part of the surgical procedure. The present inventors have recognized that this requirement to provide the conductive fluid is a drawback since in some cases fluid obscures the surgical field; it somewhat complicates the surgical procedure, and unless the conductive fluid is kept replenished it may cause a breakdown in the plasma regime, thus interfering with the cutting. Also, electric current flowing through the conductive fluid away from the tissue results in unnecessary power dissipation and associated increase in collateral tissue damage.
An additional technical problem is that electrosurgical equipment typically is used for three main classes of procedures. First, there is cutting of tissue. Next, there is coagulation (sealing) of blood vessels. Next, there is fulguration or ablation which is a species of coagulation typically involving somewhat different levels of heat application, but also for sealing or closing tissue. Some existing electrosurgical equipment provides all of these. However, the amount and type of electrical energy applied for each of these is different and all-purpose devices are generally somewhat unsatisfactory. Moreover, combining such functions in one device is problematic since the types of RF energy applied to achieve the plasma typically differ substantially for each of the three.